The present invention relates to a semiconductor integrated circuit device, and a method of manufacturing the same. More particularly, it relates to techniques which are effective when applied to a semiconductor integrated circuit device having a nonvolatile memory.
A nonvolatile memory cell of the one-element type has been proposed as the nonvolatile memory cell of an EEPROM (Electrically Erasable Programmable Read Only Memory). This nonvolatile memory cell is constructed of a field-effect transistor (MISFET) which has a floating gate electrode (information storing gate electrode) and a control gate electrode (controlling gate electrode). The source region of the MISFET is connected to a source line, and the drain region to a data line.
The nonvolatile memory cell is called a "flash type nonvolatile memory cell", in which information is written with hot electrons and is erased by tunneling. More specifically, the information writing operation of the nonvolatile memory cell is carried out in such a way that hot electrons are generated by a high electric field in the vicinity of the drain region and are injected into the floating gate electrode. On the other hand, the information erasing operation of the nonvolatile memory cell is carried out in such a way that the electrons stored in the floating gate electrode are emitted into the source region by the Fowler-Nordheim type tunneling.
Since the area of the flash type nonvolatile memory cell can be reduced owing to the single-element type as stated above, the EEPROM configured of the cells has the feature that a larger memory capacity can be achieved.
By the way, the EEPROM mentioned above is explained in "1988 IEEE International Solid-State Circuits Conference", pp. 132-133 and 330.